The first week of school I lose my voice every year. I feel that by being more authoritative the first couple weeks, especially when the students are learning procedures and rules is important. I raise my voice and have a very serious expression on my face. I'm a young female teacher, so all in all I'm not intimidating-but sometimes I need to be. I had a class this year come in that were not under control for anyone. They were wild for their teacher, specialists, and subs. So the first time I met them, they were very sure to let me know who they were and what they were about. I made them put their heads down the whole period and gave them a lecture on entering my classroom correctly-a 50 minute lecture. The next week they gave me dirty looks as they gloomilly walked into my room. "Are we going to do art today?" was the question du jour. I answered "That's not really up to me as much as it is up to you." We sat down and took attendance- three times until they did so correctly. We talked about last week and what went wrong for about twenty minutes while also going over the rules and procedures. Then we painted. They were thrilled. Two weeks later they were my first class to use clay and they actually said thank you. One of the boys in that class told me "I'm only good for you and my daddy. You make me so frustrated." That made me happy. They are one of my best behaved classes now and best-loved.
I will not say whether raising your voice is right or wrong, I think it just depends on the situation.